The prior art, U.S. Pat. No. 4,002,545 entitled "Method of Forming A Thin Film Capacitor" granted Jan. 11, 1977 to F. P. Fehiner et al., proposed a thin film capacitor comprising a dual bottom electrode, a tantalum oxide film formed on the bottom electrode, and a counter electrode. The duplex bottom electrode consists of a first layer of any electrically conductive material which is compatible with tantalum and tantalum oxide, such as aluminum, nichrome, chromium, and gold, and a second layer of tantalum.
U.S. Pat. No. 3,969,197 entitled "Method For Fabricating A Thin Film Capacitor" granted July 13, 1976 to N. J. Tolar et al., discloses a thin film capacitor having a dual bottom electrode which consists of a first layer of molybdenum or tungsten and a second layer of chromium, on which is deposited a dielectric film of tantalum oxide. The materials used are selected so that they all have substantially the same coefficient of thermal expansion. These dual bottom electrodes of the prior art are not satisfactory for use in the VLSI devices, particularly when they are used for decoupling capacitors since they are subject to corrosion or oxidation during high temperature deposition of CVD Si.sub.3 N.sub.4 or SiO.sub.2.
U.S. patent application Ser. No. 182,740 entitled "Capacitor structures With Dual Dielectrics" by J. K. Howard, filed Aug. 29, 1980 and assigned to the assignee of this invention relates to a thin film capacitor wherein the dielectric film is comprised of a first dielectric layer of silicon nitride of aluminum oxide and a second dielectric layer selected from the group consisting of Ta.sub.2 O.sub.5, HfO.sub.2, TiO.sub.2, PbTiO.sub.3, BaTiO.sub.3, CaTiO.sub.3, and SrTiO.sub.3. The bottom electrode was polycrystalline silicon which could easily withstand the 800.degree. C. process for CVD Si.sub.3 N.sub.4. However, if this capacitor structure is used for a thin film decoupling capacitor, polysilicon is not acceptable since the sheet resistance of phosphorus doped polysilicon is approximately 20-40 ohms/square, whereas the sheet resistance requirement for the bottom electrode in the decoupling capacitor is 10-30.times.10.sup.-2 ohms per square.
U.S. Pat. No. 3,723,838 entitled "Nitrogen-Doped Beta Tantalum Capacitor" granted Mar. 27, 1973 to H. Y. Kumagai and U.S. Pat. No. 3,621,347 entitled "Semi-conductor Device Comprising A Field Effect Transistor Having An Insulated Gate Electrode and Circuit Arrangement Comprising Such a Semiconductor Device" granted Nov. 16, 1971 to J. A. Van Nielen generally relate to thin film capacitors.